While a vehicle is traveling, its passenger compartment can sometimes make abnormal noises which are not supposed to be generated therein. Such abnormal noises include chatter (noise produced when vehicle body components or small parts are vibrated and brought into contact with each other when the engine vibrates) of the instrument panel, for example. When the vehicle manufacturer or car repair shop is asked to repair the vehicle to stop the chatter, the field service person diagnoses the vehicle while actually driving the vehicle in order to confirm how and where the noise is produced. Alternatively, the field service person puts the vehicle on a vibration exciter, forcibly vibrates the vehicle to reproduce the abnormal sound, confirms the position where it is generated, and diagnoses the vehicle (Japanese Patent No. 3885297).